Flavonoid solubilizing agent and method of solubilizing flavonoid

ABSTRACT

A flavonoid solubilization agent capable of highly solubilizing flavonoids such as isoflavone, baicalin, rutin and naringin whose solubility is generally low; and a method of effecting the above solubilization. Flavonoids can be solubilized by causing a flavonoid and soybean saponin and/or malonyl isoflavone glycoside to be co-present in an aqueous medium.

TECHNICAL FIELD

The present invention relates to a flavonoid solubilizing agent capableof highly solubilizing flavonoids whose solubility is generally low; anda method of effecting the solubilization.

BACKGROUND ART

Patent Document 1: JP 04-27823 B

Patent Document 2: JP 03-27293 A

Patent Document 3: JP 3060227 B2

Patent Document 4: JP 05-176786 A

Patent Document 5: JP 07-107972 A

Patent Document 6: JP 10-101705 A

Patent Document 7: JP 09-309902 A

Patent Document 8: JP 10-298175 A

Patent Document 9: JP 2003-195 A

Non-Patent Document 1: Planta Med, 67 (1), 49-54, 2001

Flavonoids are aromatic compounds whose basic structure is a phenylchroman skeleton (C6-C3-C6/A ring-C ring-B ring), and are classifiedinto flavones, flavonols, flavanones, flavanonols, isoflavones,anthocyanins, flavanols, chalcones, aurones and the like in accordancewith the difference in the C ring moieties. In recent years, as theelucidation of a variety of functionalities of natural componentsproceeds, the physiological functions of flavonoids have been noted of.However, many of flavonoids are slightly soluble in water, in foodproducts, particularly in drinks and the like, the problems such ascloudiness, sedimentation and the like are caused during the productionand storage, and this makes their industrial utilization difficult.

Hitherto, as known methods of solubilizing flavonoids, there are amethod of converting isoflavone, rutin, hesperidin or the like intoα-glycosyl isoflavonoid, α-glycosyl rutin, α-glycosyl hesperidin or thelike by reacting α-glycosyl transferase with it (see Patent Documents1-3), a method of obtaining catechin glycosides by reacting sucrosephosphorylase with a mixture of catechins and glycose-1-phosphoric acidor sucrose (Patent Document 4), a method of forming glycosides bysolubilizing flavonoids in an alkali region of pH 8 or more and/or byaddition of a cyclodextrin, and subjecting the solubilized product toglycotransfer with a cyclodextrin synthetic enzyme (Patent Document 5),a method of dissolving flavonoids in strong alkali solution and addingthe resultant to a thickening polysaccharide solution (see PatentDocument 6), a method of forming an inclusion product of isoflavone withcyclodextrin (Patent Documents 7 and 8) and the like are known.

However, any of the above-described methods is that for solubilizing aspecific flavonoid, or that for enhancing the solubility of a specificflavonoid by structure conversion, and is not to provide a method forsolubilizing flavonoids in general existing in nature as a basictechnology. This is a problem from the viewpoint of versatility. In themethods of Patent Documents 7 and 8, since the solubility ofcyclodextrin itself is not so high, the amount to be added is limited,and if a large amount is added, the cyclodextrin forms an inclusioncompound with a flavoring agent, etc., and therefore the product designsuch as flavoring of foods, etc. are hindered.

On the other hand, isoflavones exist mainly in the form of glycosides inlegumes and irises. Specifically, there are daidzin, genistin, glycitin,their malonyl glycosides such as 6″-O-malonyl daidzin, 6″-O-malonylgenistin and 6″-O-malonyl glycitin, their acetyl glycosides such as6″-O-acetyl daidzin, 6″-O-acetyl genistin, 6″-O-acetyl glycitin, theiraglycons such as daidzein, genistein and glycitein, and the like. Whileisoflavones are also in general slightly soluble in water, among them,the malonyl glycosides are known to have relatively soluble nature inwater because they have dissociation groups on their side chains.However, it has not been known so far that the malonyl glycosides havean activity of solubilizing isoflavones, much less other flavonoids.

Saponins are classified mainly into steroid saponins and triterpenoidsaponins from the viewpoint of their chemical structures. Quillaiasaponin, soybean saponin, and enju saponin which are triterpenoidsaponins are known to be natural emulsifiers for foods. Patent Document9 discloses a technology for solubilizing a ginkgo leaf extractcontaining quercetin, etc. by using saponins together with glycerin,saccharides, etc., and teaches that quillaia saponin is preferredbecause quillaia saponin is particularly excellent in a surfactantcapability. However, since there is a report that saponins are weak inan activity for solublizing a slightly soluble compound in water such asrutin, etc., and in general, should not be used as solubilizing agents(Non-Patent Document 1), it is unknown whether or not saponins have ahigh activity for solubilizing flavonoids and high versatility, even iftheir surfactant capability is high.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

An object of the present invention is to provide a novel method ofsolubilizing slightly soluble flavonoids.

Means for Solving the Problem

The present inventors have studied intensively the above-describedproblem. As a result, the present inventors have unexpectedly foundthat, when having a flavonoid coexist with a soybean saponin or amalonyl isoflavone glycoside in an aqueous medium, the solubility of theflavonoid in water is improved and further, when having a flavonoidcoexist with a soybean saponin and a malonyl isoflavone glycoside, thesolubility of the flavonoid is further improved depending on aparticular kind of a flavonoid. Thus, the present invention has beencompleted.

That is, the present invention relates to a method of solubilizingflavonoid(s) which comprises having the flavonoid(s) coexist with asoybean saponin and/or a malonyl isoflavone glycoside in an aqueousmedium.

EFFECT OF THE INVENTION

The method of the present invention is a quite versatile and easilyoperable method applicable to solubilization of naturally occurringflavonoids in general which are slightly soluble in water by an easyoperation without requiring troublesome processing treatment to obtain atransparent material. Furthermore, since the solubilized flavonoid canbe maintained for a long period of time at a lower temperature withoutformation of a precipitate, the method of the present invention is veryadvantageous from the viewpoint of storage stability and refrigerationstability.

Function

Although the solubilization mechanism of flavonoids by the method of thepresent invention has not been elucidated, it is presumed that a soybeansaponin would form mixed micelles with flavonoids in an aqueous mediumto solubilize the flavonoids. Further, as for a malonyl isoflavoneglycoside, it is presumed that the solubilizing force to water would beenhanced by hydrophobic interaction between the aromatic rings eachother to increase an affinity for flavonoids. Then, when both componentscoexist, it is presumed that the solubilizing force would besynergistically enhanced depending on a particular kind of a flavonoid.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be specifically illustrated.First, examples of the flavonoids in the present invention includeflavones (flavone, apigenin, luteolin, biacalein, chrysin and the like),flavonols (kaempferol, quercetin, miricetin and the like), flavanones(hesperetin, naringin, liquiritigenin and the like), flavanolols(alpinone, taxifolin and the like), isoflavones (daidzein, genistein,glycitein, equol, biochanin A, coumestrol, puerarin, formononetin andthe like), anthocyanins (pelargonidin, cyanidin, delphinidin, malvidin,petunidin, peonidin, petunidin and the like), flavanols (catechins suchas epicatechin, epicatechin gallate, epigallocatechin, epigallocatechingallate, theaflavin and the like, leukoanthocyanidin and the like),chalcones (carthamine, phloretin and the like), aurones (aurocidine andthe like), and the like, their glycosides and analogs. However, theflavonoids are not limited thereto, and the method of the presentinvention can be widely applied to all flavonoids. These flavonoids ingeneral are slightly soluble in water.

Next, the method of solubilizing flavonoid(s) will be illustrated. Forsolubilizing flavonoid(s), one can simply have the flavonoid(s) coexistwith a soybean saponin and/or a malonyl isoflavone glycoside in anaqueous medium, and it is preferable that both malonyl isoflavoneglycoside and soybean saponin are used together, thereby obtaining anexcellent solubilizing capability and versatility.

Example of the aqueous medium include water, an aqueous solution of analcohol, an aqueous solution of an alkali, and an aqueous solution towhich saccharides, fruit juices, vegetable juices, vitamins, acidulants,sweetening agents, salts and the like are added. Further, the aqueousmedium may be oil-in-water type emulsified emulsions such as milk andthe like. Suitably, in order to enhance the solubility of the soybeansaponin and flavonoid(s), the aqueous medium preferably has pH of 5 ormore, preferably pH 6 to 8.

For having the flavonoid(s) coexist with the soybean saponin and/or themalonyl isoflavone glycoside in the aqueous medium, any method can beemployed and examples thereof include a general method such as stirringor homogenizing an aqueous medium containing the flavonoid(s), soybeansaponin and/or malonyl isoflavone glycoside.

At this time, in order to enhance the solubility of flavonoid(s) uponcoexistence with the soybean saponin and/or the malonyl isoflavoneglycoside, preferably, the aqueous medium is subjected to heattreatment, and the heating conditions can be set by taking thesolubility of flavonoid(s) to be treated into consideration. Usually, itis sufficient to carry out the heat treatment at 60° C. to 150° C. forabout several seconds to about one hour. Needless to say, the heattreatment can be carried out as sterilization during the productionsteps of a product such as a drink or the like.

In addition, the flavonoid(s) may be previously dissolved in analiphatic alcohol having 1 to 4 carbon atoms or its solution in awater-containing solvent, an alkali solution or the like, followed byhaving the dissolved flavonoid(s) coexist with the soybean saponin andthe malonyl isoflavone glycoside in the aqueous medium.

The soybean saponin is also referred to as a soyabean saponin, andexamples thereof include group A saponin, group B saponin, group Esaponin, DDMP saponin and the like. Its structure is different from thatof a quillaia saponin or the like. In the present invention, thesesaponins may be used alone or in combination. Among them, group Asaponin is bis-desmoside saponin, and its solubilizing capability isparticularly high. Then, it is preferable that 50% or more of thesoybean saponin to be used is group A saponin. Therefore, although amethod of preparing a material containing a soybean saponin to be usedin the present invention is not particularly limited, most preferably,soybean hypocotyls are extracted with a solvent such as water,water-containing alcohol or the like, followed by being appropriatelypurified. Further, the present invention also includes the use of acomposition mainly containing a soybean saponin and, for example,commercially available “Soy Health SA” which contains about 50% ofsoybean saponin (among them, about 33% is group A saponin) (manufacturedby Fuji Oil Company, Limited) and the like can be used.

As a malonyl isoflavone glycoside, for example, 6″-O-malonyl daidzin,6″-O-malonyl genistin, 6″-O-malonyl glycitin and the like can be usedalone or in combination. Since these malonyl isoflavone glycosides havemalonyl group in their side chains, these malonyl isoflavone glycosideshave the nature of being relatively soluble in water among theseisoflavones. Although a method of preparing a malonyl isoflavoneglycoside is not particularly limited, soybean hypocotyls are extractedwith a solvent such as water, water-containing alcohol or the like,followed by being appropriately purified. Further, of course, thepresent invention includes the use of a composition mainly containing amalonyl isoflavone glycoside and, for example, commercially available“Soya Flavone HG” containing about 20% of a malonyl isoflavone glycoside(manufactured by Fuji Oil Company, Ltd.) can be used.

Suitably, the amount of a soybean saponin to be used is 5% by weight ormore, more preferably 30 to 300% by weight as dry weight ratio relativeto the flavonoid(s). If the amount to be added small, the flavonoid(s)are insufficiently solubilized, and on the contrary, if the amount to beadded is too large, it is uneconomical.

In the case where a soybean saponin and a malonyl isoflavone glycosideare used in combination, suitably, the amount of the soybean saponin andthe malonyl isoflavone glycoside to be used is 5% by weight or more,more preferably 30 to 300% by weight as dry weight ratio relative to theflavonoid(s).

The amount of the flavonoid(s) to be used can be appropriately adjustedin accordance with the purpose, however, in order to obtain the maximumdissolution of flavonoid(s), an excessive amount of flavonoid(s) areadded to and saturated in the aqueous medium, and then the solid mattercan be removed by filtering and so on. Flavonoid(s) which have beensolubilized in this way are transparently dissolved and are alsoexcellent in stability in the aqueous medium. In the case thatsufficient stability is also required under refrigeration conditions,preferably, a mixture of flavonoids(s), a soybean saponin and/or amalonyl isoflavone glycoside is previously cooled to a lower temperatureprior to filtration of the solid matter.

The above-described solubilization method can be used in the productionsteps of the following products, thereby solubilizing the flavonoid(s)to obtain flavonoid-containing products having high storage stability.

Further, there can be provided as a flavonoid solubilizing agent byutilizing the solubilizing capability of a soybean saponin and/or amalonyl isoflavone glycoside, that is, by utilizing these pure materialsor a preparation containing them as such, or optionally together withadditives such as a saccharide, emulsifier and the like. This flavonoidsolubilizing agent can be provided by processing it into a variety offorms such as powder, liquid and the like.

Moreover, there can be provided a solubilized flavonoid composition byutilizing the flavonoid solubilizing capability of a soybean saponinand/or a malonyl isoflavone glycoside, having flavonoid(s) coexist witha soybean saponin and/or a malonyl isoflavone glycoside in an aqueousmedium and, if necessary, subjecting the resultant mixture to heattreatment to obtain a solubilized flavonoid solution. The solution assuch or after processing it into powder can be used as the composition.Since the obtained solubilized flavonoid composition is extremely highin water-solubility at ordinary temperature, it can be added as it isand utilized during the production of a variety of products,particularly liquid products, for example, foods and drinks, medicines,quasi drugs, cosmetics, oral preparations, dentifrices, aromatic agents,deodorants, detergents and the like. Among these, it is advantageous toutilize the composition for healthy foods and drinks to which a varietyof physiological functions that flavonoids have are given.

Hereinafter, Examples will be described, however, the technologicalconcept of the present invention is not limited to theseexemplifications.

EXAMPLE 1

Ultrapure water 10 mL was added to commercially available baicalin(flavones, purity; 90% or more, manufactured by Wako Pure Chemicals,Co., Ltd.) 100 mg, and a commercially available malonyl glycoside-richsoybean isoflavone (trade name “Soya Flavone HG”, manufactured by FujiOil Company, Limited) 100 mg as a solubilizing agent (containing 20 mgof soybean saponin, 15 mg of group A saponin, and 20 mg of malonylisoflavone glycoside), or a commercially available soybean saponin(trade name “Soy Health SA”, manufactured by Fuji Oil Company, Limited)100 mg (containing 50 mg of soybean saponin, and 33 mg of group Asaponin), and the mixture was stirred at 80° C. for one hour. Then,after the mixture was equilibrated at 10° C. for 48 hours, thesupernatant was collected by centrifugation. The OD₂₅₄ of thesupernatant was measured and the dissolution amount of baicalin wascalculated by the following equation 1.baicalin dissolution amount (mg/100 mL)=(OD₂₅₄ in samplesupernatant−OD₂₅₄ in control supernatant)/baicalin specificabsorbance×1000

Further, the supernatant was placed in a test tube and, after it waspasteurized by heating at 95° C. for 15 minutes, it was stored at 10° C.for one month to observe the formation of a precipitate by visualexamination. TABLE 1 Solubilizing Baicalin dissolution Storage agentamount (mg/100 mL) stability (10° C.) without additive 12.4 precipitateSoya Flavone HG 130.6 no precipitate Soy Health SA 75.9 no precipitate

The soybean saponin, or the soybean saponin and the malonyl isoflavoneshowed a high solubilizing capability with respect to baicalin. Thesolubilizing magnifying power indicated 10.5-fold in the co-presence ofthe soybean saponin/the malonyl isoflavone glycoside relative tobaicalin alone, and indicated 6.1-fold in the co-presence of the soybeansaponin. The baicalin solution thus solubilized showed excellentstability without formation of a precipitate during storage underrefrigeration.

EXAMPLE 2

Ultrapure water 10 mL was added to commercially available rutin(flavonols, purity: 90% or more, manufactured by Wako Pure Chemicals,Co., Ltd.) 100 mg and the same solubilizing agent as that used inExample 1, and the mixture was stirred at 80° C. for one hour. Then,after it was equilibrated at 10° C. for 48 hours, the supernatant wascollected by centrifugation. The OD₂₅₄ of the supernatant was measuredand a rutin dissolution amount was calculated by the following equation2.rutin dissolution amount (mg/100 mL)=(OD₂₅₄ in sample supernatant−OD₂₅₄in control supernatant)/rutin specific absorbance×1000

Further, the supernatant was placed in a test tube, after it waspasteurized by heating at 95° C. for 15 minutes, it was stored at 10° C.for one month to observe the formation of a precipitate by visualexamination. TABLE 2 Solubilizing Rutin dissolution Storage agent amount(mg/100 mL) stability (10° C.) without additive 3.0 precipitate SoyaFlavone HG 90.3 no precipitate Soy Health SA 117.7 no precipitate

The soybean saponin, or the soybean saponin and the malonyl isoflavoneshowed a high solubilizing capability with respect to rutin. Thesolubilizing magnifying power indicated 30.1-fold in the co-presence ofthe soybean saponin/the malonyl isoflavone glycoside relative to rutinalone, and indicated 39.2-fold in the co-presence of the soybeansaponin. The rutin solution thus solubilized showed excellent stabilitywithout formation of a precipitate during the storage.

EXAMPLE 3

Ultrapure water 10 mL was added to commercially available hesperidin(flavanones, purity: 92% or more, manufactured by Wako Pure Chemicals,Co., Ltd.) 100 mg and the same solubilizing agent as that used inExample 1, and the mixture was stirred at 80° C. for one hour. Then,after it was equilibrated at 10° C. for 48 hours, the supernatant wascollected by centrifugation. The OD₂₅₄ of the supernatant was measuredand a hesperidin dissolution amount was calculated by the followingequation 3.hesperidin dissolution amount (mg/100 mL)=(OD₂₅₄ in samplesupernatant−OD₂₅₄ in control supernatant)/hesperidin specificabsorbance×1000

Further, the supernatant was placed in a test tube, and after it waspasteurized by heating at 95° C. for 15 minutes, it was stored at 10° C.for one month to observe the formation of a precipitate by visualexamination. TABLE 3 Solubilizing Hesperidin dissolution Storage agentamount (mg/100 mL) stability (10° C.) without additive 8.6 precipitateSoya Flavone HG 78.0 no precipitate Soy Health SA 78.0 no precipitate

The soybean saponin, or the soybean saponin and the malonyl isoflavoneshowed a high solubilizing capability with respect to hesperidin. Thesolubilizing magnifying power indicated 9.1-fold in the co-presence ofthe soybean saponin/the malonyl isoflavone glycoside with respect tohesperidin alone, and indicated 9.1-fold in the co-presence of thesoybean saponin. The hesperidin solution thus solubilized showedexcellent stability without formation of a precipitate during thestorage.

EXAMPLE 4

Ultrapure water 10 mL was added to commercially available naringin(flavanones, purity: 95% or more, manufactured by Sigma Inc.) 100 mg andthe same solubilizing agent as that used in Example 1, and the mixturewas stirred at 80° C. for one hour. Then, after it was equilibrated at10° C. for 48 hours, the supernatant was collected by centrifugation.The OD₂₅₄ in the supernatant was measured and a naringin dissolutionamount was calculated by the following equation 4.naringin dissolution amount (mg/100 mL)=(OD₂₅₄ in samplesupernatant−OD₂₅₄ in control supernatant)/naringin specificabsorbance×1000

Further, the supernatant was placed in a test tube, and after it waspasteurized by heating at 95° C. for 15 minutes, it was stored at 10° C.for one month to observe the formation of a precipitate by visualexamination. TABLE 4 Solubilizing Naringin dissolution Storage agentamount (mg/100 mL) stability (10° C.) without additive 68.0 precipitateSoya Flavone HG 975.0 no precipitate Soy Health SA 980.0 no precipitate

The soybean saponin or the soybean saponin and the malonyl isoflavoneshowed a high solubilizing capability with respect to naringin. Thesolubilizing magnifying power indicated 14.3-fold in the co-presence ofthe soybean saponin/the malonyl isoflavone glycoside with respect tonaringin alone, and indicated 14.4-fold in the co-presence of thesoybean saponin. The naringin solution thus solubilized showed excellentstability without formation of a precipitate during the storage.

EXAMPLE 5

Ultrapure water 10 mL was added to a commercially available soybeanisoflavone (trade name “Honen Isoflavone-80”, manufactured by HonenCorporation) 125 mg (100 mg of isoflavone glycoside) and the samesolubilizing agent as used in Example 1 and the mixture was stirred at80° C. for one hour. Then, after it was equilibrated at 10° C. for 48hours, the supernatant was collected by centrifugation and an isoflavonedissolution amount was measured by HPLC. Further, the supernatant wasplaced in a test tube, and after it was pasteurized with heating at 95°C. for 15 minutes, it was stored at 10° C. for one month to observe theformation of a precipitate by visual examination. TABLE 5 SolubilizingIsoflavone amount Storage agent (mg/100 mL) stability (10° C.) withoutadditive 25.6 precipitate Soya Flavone HG 698.4 no precipitate SoyHealth SA 215.8 no precipitate

The soybean saponin, or the soybean saponin and the malonyl isoflavoneindicated a high solubilizing capability with respect to the isoflavone(slightly soluble isoflavone other than malonyl isoflavone glycoside).The solubilizing magnifying power indicated 27.3-fold in the co-presenceof the soybean saponin/the malonyl isoflavone glycoside, and indicated84.4-fold in the co-presence of the soybean saponin with respect to theisoflavone alone. The isoflavone solution thus solubilized showedexcellent stability without formation a precipitate during the storage.

EXAMPLE 6

Ultrapure water 1 mL was added to a commercially available soybeanisoflavone (trade name “Honen Isoflavone-80”, manufactured by HonenCorporation) 12.5 mg (10 mg of isoflavone glycoside) and a commerciallyavailable malonyl isoflavone glycoside, malonyl daidzin (purity: 90% ormore, manufactured by Wako Pure Chemicals, Co., Ltd.) 1 mg, and themixture was stirred at 25° C. for one hour. Then, after it wasequilibrated at 10° C. for 48 hours, the supernatant was collected bycentrifugation and an isoflavone dissolution amount was measured byHPLC. Further, the supernatant was placed in a test tube, it was storedas such at 10° C. for one month to observe the formation of aprecipitate by visual examination. TABLE 6 Solubilizing Isoflavoneamount Storage agent (mg/100 mL) stability (10° C.) without 17.3precipitate additive Malonyl daidzin 106.3 No precipitate (including56.9 of malonyl daidzin)

One of malonyl isoflavones, i.e., malonyl diazin alone also showed ahigh solubilizing capability with respect to the isoflavone glycoside.Since the dissolution amount of malonyl daidzin itself is 56.9 mg/100mL, the solubilizing magnifying power of the isoflavone glycosideindicated 2.9-fold in the co-presence of malonyl daidzin. The isoflavonesolution thus solubilized showed excellent effect stability withoutformation of a precipitate during the storage.

EXAMPLE 7

Ultrapure water 10 mL was added to a commercially available soybeanisoflavone (trade name “Honen Isoflavone-80”, manufactured by HonenCorporation) 125 mg (100 mg of isoflavone glycoside) and the samecommercially available malonyl-rich soybean isoflavone as that used inExample 1, 100 mg, 300 mg, or 1000 mg, or the same commerciallyavailable soybean saponin as that used in Example 1, 100 mg, 300 mg, or1000 mg, and the mixture was stirred at 80° C. for one hour.Subsequently, after it was equilibrated at 10° C. for 48 hours, thesupernatant was collected by centrifugation and an isoflavonedissolution amount was measured by HPLC. Further, the supernatant wasplaced in a test tube, and after it was pasteurized by heating at 95° C.for 15 minutes, it was stored at 10° C. for one month to observe theformation of a precipitate by visual examination. TABLE 7 Malonyisoflavone Soybean Isoflavone glycoside saponin dissolution StorageSolubilizing content content amount stability agent (mg/100 mL) (mg/10mL) (mg/100 mL) (10° C.) without 0 0 25.6 precipitate additive Soya 2020 697.2 no Flavone HG precipitate 60 60 1502.3 no precipitate 200 2004405.6 no precipitate Soy Health 0 50 213.7 no SA precipitate 0 150329.4 no precipitate 0 500 764.9 no precipitate

The malonyl isoflavone or the soybean saponin showed a solubilizingcapability with respect to the isoflavone (slightly soluble isoflavoneother than malonyl isoflavone) in a concentration-dependent manner. Thesolubilizing magnifying power indicated 172-fold at maximum in theco-presence of the malonyl isoflavone and 30-fold at maximum in theco-presence of the soybean saponin. The isoflavone solution thussolubilized showed excellent without formation of a precipitate duringthe storage.

EXAMPLE 8

The solubilizing capability between a soybean saponin and a variety offlavonoids of quillaia saponin used as a surfactant were compared. Acommercially available soybean saponin powder (“Soy Health SA”,manufactured by Fuji Oil Company, Limited) or dry powder of acommercially available quillaia saponin liquid preparation (“QuillaianinS-100”, manufactured by Maruzen Pharmaceuticals, Co., Ltd.) 0.1 g, andan isoflavone (glycoside), rutin or ginkgo leaf extract (containingquercetin, kaempferol, and the like) 0.01 g were placed in a test tube.After 0.2 M Na2HPO4/0.1 M acetic acid buffer (pH7) 10 mL was addedthereto and stirred, the mixture was pasteurized with heating in aboiling water bath for 15 minutes. Then, after it was stored at 10° C.for 2 weeks, the dissolution state of the liquid thus obtained wasobserved by visual observation.

As a result, as shown in Table 8, the soybean saponin clearlysolubilized all of the isoflavone, rutin, and ginkgo leaf extract. Onthe other hand, quillaia saponin solubilized only ginkgo leaf extract.Hence, it was unexpectedly found that a solubilizing capability of thesoybean saponin with respect to the flavonoid was superior to that ofquillaia saponin and the versatility of the soybean saponin was higherthan that of quillaia saponin. TABLE 8 Solubilizing agent SoybeanQuillaia Flavonoids addition-free saponin saponin Isoflavone x ∘ x Rutinx ∘ x Ginkgo leaf x ∘ ∘ extract∘: precipitatex: no precipitate

INDUSTRIAL APPLICABILITY

The solubilization of flavonoids in general can be easily performed in ahigh degree without changing their chemical structures and physiologicaleffects by utilizing a soybean saponin and/or a malonyl isoflavoneglycoside as a solubilizing agent of the flavonoids. The presentinvention can provide a highly versatile basic technology of flavonoidsolubilization. Hence, it can be utilized particularly for wide range ofproducts which are used by dissolving flavonids, such as foods anddrinks, medicines, quasi drugs, cosmetics, oral preparations,dentifrices, aromatic agents, deodorants, detergents and the like.

1. A method of solubilizing flavonoid(s) which comprises having theflavonoid(s) coexist with a soybean saponin and/or a malonyl isoflavoneglycoside in an aqueous medium.
 2. The solubilizing method according toclaim 1, wherein the flavonoid(s) are one or more flavonoids selectedfrom flavones, flavonols, flavanones, flavanonols, isoflavones,anthocyanins, flavanols, chalcones, and aurones.
 3. A flavonoidsolubilizing agent comprising a soybean saponin and/or a malonylisoflavone glycoside.
 4. A solubilized flavonoid composition obtainableby having flavonoid(s) coexist with a soybean saponin and/or a malonylisoflavone glycoside in an aqueous medium.
 5. A flavonoid-containingproduct comprising the solubilized flavonoid composition according toclaim
 4. 6. The flavonoid-containing product according to claim 5, whichis a food or drink, a medicine, a quasi drug, a cosmetic, an oralpreparation, a dentifrice, an aromatic agent, a deodorant, or adetergent.
 7. The flavonoid-containing healthy food or drink accordingto claim 5, which has the physiological function(s) of the flavonoid(s).8. A process for producing a flavonoid-containing product, whichcomprises the steps of adding flavonoid(s), and a soybean saponin and/ora malonyl isoflavone glycoside to an aqueous medium; and then subjectingthe resulting mixture to heat treatment to solubilize the flavonoid(s).9. The process according to claim 8, wherein the flavonoid-containingproduct is a food or drink, a medicine, a quasi drug, a cosmetic, anoral preparation, a dentifrice, an aromatic agent, a deodorant, or adetergent.
 10. The process for producing a flavonoid-containing healthyfood or drink according to claim 8, to which the physiologicalfunction(s) of the flavonoid(s) have been imparted.